If RAILS_ENV is set to anything that is not configured on logger.yaml, rails fails to load with a message:

`deep_merge!': undefined method `each_pair' for nil:NilClass (NoMethodError)
        from /home/daniel/.rbenv/versions/2.1.5/lib/ruby/gems/2.1.0/gems/activesupport-3.2.21/lib/active_support/core_ext/hash/deep_merge.rb:10:in `deep_merge'
        from /home/daniel/workspace/cleanforeman/lib/foreman/logging.rb:78:in `load_config'
        from /home/daniel/workspace/cleanforeman/lib/foreman/logging.rb:17:in `configure'

The message should be clearer or we should use the default on environments not defined in logger.yaml.